DEF is widely used as a cotton defoliant in California and the southern United States. DEF has produced delayed neurotoxic effects, acute cholinergic effects and late acute effect in some animal species. DEF is a frequent contaminant in water drained from agricultural land and has been shown to be toxic to fish at low concentration under acute exposure (ppm). With chronic exposure, DEF has been shown to adversely affect the survival of some species of fish at ppb levels. This study was undertaken to examine the comparative neurotoxic effects of acute DEF exposures to two aquatic species, a vertebrate, the channel cat fish and the blue crab, an invertebrate. Residues of DEF and its rate of disappearance were also determined in certain tissues of these animals.